1. Field of the Invention
The present invention generally relates to a flash fixing color toner that is used with an image forming process which is performed by an electrophotographic copier, facsimile or printer, and more particularly to a flash fixing color toner which is fixed to a recording medium by irradiation of flash light in an electrophotographic image forming process. Further, the present invention relates to an image forming process that uses the flash fixing color toner which is fixed to a recording medium by irradiation of flash light.
2. Description of the Related Art
In an electrophotographic image forming apparatus that employs flash light irradiation for fixing a toner onto a recording medium, the application of pressure to the toner is not needed for the fixing of the toner but it is necessary to make efficient use of the energy of flash light in the fixing or fusing of the toner onto the recording medium.
Generally, a color toner absorbs only part of an irradiation light energy, apart from a black toner. It has been observed that the light energy absorption properties of a color toner are lower than the light energy absorption properties of a black toner, and that the use of a color toner in a conventional flash fixation process often causes a defective fixing. However, in recent years, there is an increasing demand for a color image formation using an electrophotographic flash fixation process, which is capable of performing a high-speed operation and usable with a special recording medium having a step-like surface.
There are basically five major steps employed in the electrophotographic printing process: (1) charging a photoconductor electrostatically, (2) exposing the photoconductor to the imaging light pattern to create an electrostatic latent image thereon, (3) developing the photoconductor by bringing charged toner particles to the surface of the photoconductor to create a toner image thereon, (4) transferring the toner image from the photoconductor surface to a recording medium (e.g., paper), and (5) fixing or fusing the toner to the recording medium.
As is well known, among these steps of the electro-photographic printing process, the toner fixing step may be achieved by selecting one of the three methods: the heat roll method, the oven fixing method and the flash fixing method. The flash fixing method uses irradiation of light or infrared rays (flash light).
The heat roll method mentioned above is most commonly utilized. In the heat roll method, the fixing roller held at a high temperature applies heat and pressure directly to the toner so that the toner is fixed to the recording medium. With a simple, inexpensive configuration of the fixing roller used, the fixing surface can be made flat. However, there are several problems with the heat roll method. The recording medium (e.g., paper) after the toner fixing step is liable to be curled. The toner sticks to the surface of the fixing roller, and the recording medium is liable to being stained with such toner due to the offset. The recording medium and the fixing roller contact each other, and the transport of the recording medium in an image forming apparatus may be slanted from the desired direction. It is difficult to achieve high-speed image formation with the image forming apparatus. It is difficult that the heat roll method achieves the toner fixing of a special recording medium like a sticker post card.
The flash fixing method mentioned above is a non-contact toner fixing method, and the problems of the heat roller method such as the curling and the offset are eliminated. The high-speed image formation and the toner fixing of a special recording medium can easily be achieved with the flash fixing method. Accordingly, the application of the flash fixing method to high-speed printers and copiers for office use is increasing in recent years.
In the flash fixing method, a black toner or the like efficiently absorbs an irradiation light energy with respect to all the wavelengths. A thermal energy produced by irradiation of flash light will easily increase the temperature of the black toner to the desired level, and the particles of the black toner can be fused without difficulty. The toner fixing to the recording medium can easily be achieved in the case of the black toner or the like.
However, as described above, the light energy absorption properties of a color toner are lower than the light energy absorption properties of a black toner, and the use of a color toner in the conventional flash fixation process often causes a defective fixing. A thermal energy produced by irradiation of flash light does not increase the temperature of the color toner to a sufficiently high level, and the particles of the color toner cannot easily be fused. The toner fixing to the recording medium is not easily be achieved in the case of the color toner. The use of a color toner in the conventional flash fixation process is likely to cause a defective fixing (e.g., fogging).
As disclosed in International Publication No. WO99/13382 and Japanese Laid-Open Patent Application Nos.2000-147824, 7-191492, 2000-155439, 6-348056, 10-39535, 2000-35689, 11-38666, 11-125930, 11-125928, 11-125929, and 11-65167, the inclusion of an infrared absorbent in a flash fixing color toner has been proposed in order eliminate the above problem. In the conventional color toner, as disclosed in the above-mentioned documents, the use of the infrared absorbent provides the color toner with improved light energy absorption properties.
However, in the conventional color toner, only the positive ions of the infrared absorbent, which serve to improve the light energy absorption properties of the color toner, are considered. However, there is no teaching in the above-mentioned documents that the negative ions of the infrared absorbent, contained in the color toner, may affect the charged condition of the toner over an extended period of time, which will deteriorate the quality of a resulting color image.
In order to achieve the sharpness of a resulting color image, it is necessary that not only the fixing properties of the color toner are improved but also the charged condition of the color toner be controlled appropriately. Generally, in order to appropriately control the charged condition of the color toner, a charge control agent is added to the color toner. However, it has been observed that, even when the charge control agent is added to the color toner as in the above-mentioned documents, the charge control agent does not serve to suitably control the charged condition of the toner over an extended period of time, and a defective fixing (e.g. fogging) of the color toner to the recording medium is caused, which will deteriorate the quality of a resulting color image.
According to the studies conducted by the present inventors, it is estimated that the negative ions of the infrared absorbent, contained in the color toner, gradually deteriorate the properties of the charge control agent with the passage of time and affect the charged condition of the toner over an extended period of time, which causes the deterioration of the quality of the resulting color image. Specifically, when the negative ions, such as perchloric acid ion (ClO4xe2x88x92), boron-fluoric acid ion (BF4xe2x88x92), trichloroacetic acid ion (CCl3COOxe2x88x92), trifluoroacetic acid ion (CF3COOxe2x88x92), picric acid ion ((NO2)3C6H2Oxe2x88x92), hexafluoro-bromic acid ion (AsF6xe2x88x92), hexafluoro-antimonic acid ion (SbF6xe2x88x92), benzensulfonic acid ion (C6H5SO3xe2x88x92), ethanesulfonic acid ion (C2H5SO3xe2x88x92), phosphoric acid ion (PO42xe2x88x92), sulfuric acid ion (SO42xe2x88x92) or chlorine ion (Clxe2x88x92), are used in the color toner together with the charge control agent, the negative ions serve to deteriorate the properties of the charge control agent to maintain the charged condition of the toner at the desired level.
Further, when the charge control agent is not added to the color toner and the charged condition of the color toner is suitably controlled without the charge control agent, there is the case in which the negative ions of the infrared absorbent, contained in the color toner, gradually affect the charged condition of the toner over an extended period of time.
It is an object of the present invention to provide an improved flash fixing color toner in which the above-described problems are eliminated.
Another object of the present invention is to provide a flash fixing color toner that provides the sharpness of a resulting color image with good toner fixing characteristics and good developing characteristics by using an infrared absorbent which does not lower the charged condition of the toner over an extended period of time.
Another object of the present invention is to provide an image forming process that provides the sharpness of a resulting color image with good toner fixing characteristics and good developing characteristics by using a flash fixing color toner including an infrared absorbent which does not lower the charged condition of the toner over an extended period of time.
The above-mentioned objects of the present invention are achieved by a flash fixing color toner for use in an image forming process, the color toner comprising a binder resin, a coloring agent, and an infrared absorbent, wherein negative ions form part of the infrared absorbent, and the negative ions include toluenesulfonic acid ion (C6H4(CH3)SO3xe2x88x92), nitric acid ion (NO3xe2x88x92) or hexafluorophosphoric acid ion (PF6xe2x88x92).
The above-mentioned objects of the present invention are achieved by an image forming process, which is characterized by using a flash fixing color toner, the color toner comprising a binder resin, a coloring agent, and an infrared absorbent, the image forming process comprising the steps of: producing a toner image on a photoconductor by using the color toner; transferring the toner image from the photoconductor to a recording medium; and fixing the color toner to the recording medium by irradiation of flash light, so that a color image is formed on the recording medium, wherein negative ions form part of the infrared absorbent, and the negative ions include toluenesulfonic acid ion (C6H4(CH3)SO3xe2x88x92), nitric acid ion (NO3xe2x88x92) or hexafluorophosphoric acid ion (PF6xe2x88x92).
According to the flash fixing color toner of the present invention, the negative ions of the infrared absorbent, including toluenesulfonic acid ion (C6H4(CH3)SO3xe2x88x92), nitric acid ion (NO3xe2x88x92) or hexafluorophosphoric acid ion (PF6xe2x88x92), effectively prevent the lowering of the charged condition of the color toner over an extended period of time as in the conventional color toner. The stability of the charged condition of the color toner over an extended period of time is increased by the use of the infrared absorbent, and the flash fixing color toner and the image forming process of the present invention are effective in providing the sharpness of a resulting color image with good toner fixing characteristics and good developing characteristics.
Other objects, features and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings.